By nature of their location, the treatment of internal tissue defects is inherently difficult. Access to a defect through invasive surgery introduces a high level of risk that can result in serious complications for the patient. Access to the defect remotely with a catheter or equivalent device is less risky, but treatment of the defect itself is made more difficult given the limited physical abilities of the catheter. The difficulty in accessing and treating tissue defects is compounded when the defect is found in or near a vital organ. For instance, a patent foramen ovale (“PFO”) is a serious septal defect that can occur between the left and right atria of the heart and a patent ductus arteriosus (“PDA”) is an abnormal shunt between the aorta and pulmonary artery.
During development of a fetus in utero, oxygen is transferred from maternal blood to fetal blood through complex interactions between the developing fetal vasculature and the mother's placenta. During this process, blood is not oxygenated within the fetal lungs. In fact, most of the fetus' circulation is shunted away from the lungs through specialized vessels and foramens that are open during fetal life, but typically will close shortly after birth. Occasionally, however, these foramen fail to close and create hemodynamic problems, which, in extreme cases, can ultimately prove fatal. During fetal life, an opening called the foramen ovale allows blood to pass directly from the right atrium to the left atrium (bypassing the lungs). Thus, blood that is oxygenated via gas exchange with the placenta may travel through the vena cava into the right atrium, through the foramen ovale into the left atrium, and from there into the left ventricle for delivery to the fetal systemic circulation. After birth, with pulmonary circulation established, the increased left atrial blood flow and pressure causes the functional closure of the foramen ovale and, as the heart continues to develop, this closure allows the foramen ovale to grow completely sealed.
In some cases, however, the foramen ovale fails to close entirely. This condition, known as a PFO, can allow blood to continue to shunt between the left and right atria of the heart throughout the adult life of the individual. A PFO can pose serious health risks for the individual, including strokes and migraines. The presence of PFO's have been implicated as a possible contributing factor in the pathogenesis of migraine. Two current hypothesis that link PFO's with migraine include the transit of vasoactive substances or thrombus/emboli from the venous circulation directly into the left atrium without passing through the lungs where they would normally be deactivated or filtered respectively. Other diseases that have been associated with PFO's (and which could benefit from PFO closure) include but are not limited to depression and affective disorders, personality and anxiety disorders, pain, stroke, TIA, dementia, epilepsy, and sleep disorders.
Still other septal defects can occur between the various chambers of the heart, such as atrial-septal defects (ASD's), ventricular-septal defects (VSD's), and the like. To treat these defects as well as PFO's, open heart surgery can be performed to ligate and close the defect. Alternatively, catheter-based procedures have been developed that require introducing umbrella or disc-like devices into the heart. These devices include opposing expandable structures connected by a hub or waist. Generally, in an attempt to close the defect, the device is inserted through the natural opening of the defect and the expandable structures are deployed on either side of the septum to secure the tissue surrounding the defect between the umbrella or disc-like structure.
These devices suffer from numerous shortcomings. For instance, these devices typically involve frame structures that often support membranes, either of which may fail during the life of the patient, thereby introducing the risk that the defect may reopen or that portions of the device could be released within the patient's heart. These devices can fail to form a perfect seal of the septal defect, allowing blood to continue to shunt through the defect. Also, the size and expansive nature of these devices makes safe withdrawal from the patient difficult in instances where withdrawal becomes necessary. The presence of these devices within the heart typically requires the patient to use anti-coagulant drugs for prolonged periods of time, thereby introducing additional health risks to the patient. Furthermore, these devices can come into contact with other portions of the heart tissue and cause undesirable side effects such as an arrhythmia, local tissue damage, and perforation.
Accordingly, improved systems and methods for closing internal tissue defects within the heart are needed.